The two teams meet again in Portland Sunday to decide who moves on to the MLS Cup.

‘‘It’s sort of like Groundhog Day talking about this game every day for the last 12 days,’’ Porter told reporters on a conference call previewing the match.

Robbie Findley, Chris Schuler, Devon Sandoval, and Javier Morales all scored for Real Salt Lake in the opening match at Rio Tinto Stadium. The Timbers got goals from Will Johnson and Frederic Piquionne.

Portland’s loss snapped a 10-game unbeaten streak that dated to a 4-2 loss to RSL in Salt Lake Aug. 30.

Porter ticked off the reasons the Timbers think they can overcome the deficit. Portland has just one league loss at home this season. They’ve had 11 shutouts at home. They’ve scored 32 goals at home. They’ve won six matches at home by two or more goals.

If they’re successful, they’ll become the first team in 10 years to come back from a two-goal shortfall in the second match of an aggregate-goals series.

But the Timbers can’t play desperately, Porter warned.

‘‘We’re always looking to score two goals or more every single game,’’ he said. ‘‘So the worst thing we can do is look at that two-goal deficit and come out gunslinging and reckless to the point that we give up [a goal] and dig ourselves an even bigger hole.’’

Real Salt Lake has not lost to the Timbers for the past nine straight matches in all competitions. RSL’s last visit to Jeld-Wen Field resulted in a 0-0 draw.

Portland has not defeated Salt Lake since their first meeting after the Timbers joined the MLS for the 2011 season.

RSL coach Jason Kreis disagrees with the stance that all his team has to do is sit back and defend.

‘‘We want to approach the match in an aggressive fashion, but we also recognize we are leading by two,’’ he said.

Salt Lake will be without striker Alvaro Saborio, the team’s leading scorer with 12 goals this season, because of a right hip flexor injury that also kept him out of the first leg.

He did not travel to Portland, Kreis said.

‘‘We hope we can advance to give him a chance to play in the final,’’ Kreis said.

Salt Lake defender Chris Wingert is also out for Sunday’s Western Conference Championship second leg at Portland because of a broken rib and collapsed lung sustained in the first leg.

Meanwhile, Portland’s top scorer, Diego Valeri, has struggled with an adductor injury, but practiced at full speed this week, Porter said.

‘‘Today he looked as good as he has in months,’’ Porter said.

The winner will advance to the MLS Cup against the winner of Saturday night’s Eastern Conference final between Sporting Kansas City and the Houston Dynamo.

The conference winners will have another again have a two week wait until the MLS Cup match, scheduled for Dec. 7. Players accept the long layoffs for international play, Timbers midfielder Jack Jewsbury said.

‘‘On one sense, it gives guys a bit of a breather to rest the legs a little bit that first week and then get back into things, like Caleb said, and then get a bit of normalcy this week,’’ Jewsbury said. ‘‘On the other hand, we’re biting at the bit to get back on the field and play, because we weren’t extremely happy with the first leg and know we can make up for that this weekend.’’